The commit message is the one you give when doing "git commit ...".
The patch is small, so probably is faster to use the diff (https://github.com/kamailio/kamailio/commit/b84d4a1f09b6310522ac83546a7a34b2...), make a fresh clone of kamailio repo and do the commit again, with a new PR.
Otherwise, you can search on the web how to amend a commit message, but can take some time to sort out when the commit was pushed remote.